Filters and switches are often used in combination in electronic devices. In cell phones for example, radio frequency (RF) signals are detected by an antenna, converted to electrical signals, and then processed. To process the signals, a switch is needed to switch the RF antenna to a filter on the receiving side of the device, or to a filter on the transmission side of the device. In addition, switches are needed to change between frequency channels. In most electronic devices, the switches are in the form of transistors. It is known in the art of electronics that electrical signals suffer from “insertion loss” from passing through switching and filter circuitry.
SAW devices are used in certain electronic applications as resonators and filters. In a SAW filter, an electrical signal is inputted to an input SAW transducer formed on a piezoelectric substrate. The input electrical signal typically has a relatively wide range of frequencies. However, the input SAW transducer creates a SAW having only a narrow range of frequencies. The SAW then travels over the substrate and is detected by an output SAW transducer. The output SAW transducer only responds to a narrow range of SAW frequencies, further enhancing signal filtering. The detected SAW is then converted to an output electrical signal, which has a narrower frequency range than the input electrical signal.
MEMS switches are also used in select electronic applications. One example of a MEMS switch is a capacitor shunt switch, which includes a top electrode in the form of a membrane, and a bottom electrode in the form of a transmission line. In operation, when a direct current (DC) actuation voltage is applied across the top electrode (membrane) and the bottom electrode (transmission line), the membrane is deflected to make physical contact with the dielectric layer of the transmission line. This shorts the circuit to ground, thereby cutting off transmission of signals traveling through the transmission line.
Presently, both MEMS and SAW devices are employed in a variety of electronic devices as resonators, filters and switches. Yet, the general approaches to switching and filtering using SAW and/or MEMS devices involve switching in the electrical domain and filtering in the acoustic domain. This approach tends to be inefficient because of the associated insertion losses. Unfortunately, alternative approaches are currently lacking because of the dearth of efficient acoustic-based switches.